The present invention relates to a power supply control arrangement for a stepping motor of a watch disposed, in the form of an integrated circuit, between the battery and the stepping motor of the watch, which circuit, for causing a motor step under supervision of a detection system, provides for one or more power pulses controlled in such a manner that the impulses have a torque-load dependent length under normal operation and which provides, subsequent to a power pulse, a correction pulse of a reltively great length when compared to the power pulse length and which is adapted to overcome higher than normal load torques as they may occur as a result of certain disturbances.
Such motor drive control circuitry is used especially in connection with today's modern wristwatches, which must be able to operate over long periods of time and with high precision. In order to achieve the desired precision of operation it is not only necessary to maintain constant pulse intervals which is achievable by means of quartz oscillator circuits but the so-produced impulses must cause the proper advance of the stepping motor.
With older control arrangements this was achieved by providing a relatively long pulse whose energy content was large enough to cause the stepping advance even with some kind of disturbances present. As a result the battery's energy, which in a watch is only a relatively small amount, is consumed quite rapidly so that the battery needs to be replaced relatively often. In connection with modern watches it is however desirable that a battery is capable of energizing the watch's drive over a number of years, preferably for the full design life span of a watch.
In order to be able to satisfy such a requirement it is necessary to reduce the energy consumption per pulse for driving the motor, that is, duration of the pulse must be shortened. There is, however, a limit: the pulse must be sufficiently large to provide the desired rotational step of the stepping motor under normal conditions. Upon occurrence of a disturbance, however, the stepping motor would remain still. In order to prevent such malfunctions, present drive control circuits include detection systems which provide a correction signal whenever the stepping motor has not reacted to a stepping pulse. The correction signal of the detection system will cause the generation of a correction pulse which is large enough to cause a stepping advance of the stepping motor thereby overcoming the disturbance. Since, however, the usual disturbances such as the presence of dirt or undue temperatures remain often for extended periods, the load remains relatively high for those periods so that a correction signal and longer drive pulse are provided for those periods. If the extension of the drive pulse is not sufficient to provide for the desired motor step, the process described above is repeated, that is, an extended correction pulse is again provided and the drive pulse is further increased. The process may be repeated until the largest possible design drive pulse is provided. As a result, under extreme conditions, the largest design drive pulse and the large correction pulse are provided in order to achieve a desired motor step. If rotation of the stepping motor is still not obtained, these large pulses will be provided until the energy of the battery is consumed.
As a result not only will the watch be out of service but also the battery is rapidly--within a couple of weeks--drained of energy. The owner of the watch will naturally assume that the battery has to be replaced especially since, with the greater energy supply of a new battery, the watch will generally overcome the disturbance and operate for a limited time so that the actual problem is not recognized and the quite expensive batteries are replaced in short intervals.
It is therefore the principal object of the present invention to provide for a possibility of recognizing such disturbances and thereby preventing the premature and unnecessary draining of batteries.
This could be achieved by means of an energy-time sensing arrangement which would disconnect the battery if the energy consumption would the excessive over a period of time. Such an arrangement however would be relatively involved and would require substantial changes in the presently existing control circuitry. If it is desirable to avoid extensive changes of an existing control circuit such a solution cannot be utilized.